It is a mission impossible to edit a video
This has been a problem in blender for quite a while. Definately not a 2.8 problem. Not quite the optimal solution but it works is to turn the video into an image sequence and then import it as an image sequence. I usually use ffmpeg to convert the video into an image sequence but I don't know how easy that is from a non unix pc. You can always just import it into blender and export it as an image sequence. I did recently see what I think is a big improvement in the 2.8 video editor where I think this problem is fixed allthough I can't conferm because it crashed 1 second later. 
A different problem which I don't think you are describing here would be just a framerate mismach so make sure your render settings fps is the same as that of your source video. 
(If the fps counter is red the problem is probably the first one I mentioned, could still be both though)